late 14c., "to lead, direct, conduct," from Old French guider "to guide, lead, conduct" (14c.), earlier guier, from Frankish *witan "show the way" or a similar Germanic source, from Proto-Germanic *wit- "to know" (cognates: German weisen "to show, point out," Old English witan "to see"), from PIE *weid- "to see" (see vision). The form of the French word influenced by Old Provençal guidar (n.) "guide, leader," or Italian guidare, both from the same source. Related: Guided; guiding.

mid-14c., "one who shows the way," from Old French guide, 14c. (alteration of earlier guie), verbal noun from guider (see guide, v.). In book titles from 1610s; meaning "book of information on local sites" is from 1759. In 18c. France, a "for Dummies" or "Idiot's Guide to" book would have been a guid' âne, literally "guide-ass."